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Food Structure

Abstract

Microstructural changes in 8-11% wheat starch dispersions during heating, cooling and cold storage have been evaluated by light microscopy and scanning electron microscopy.

Heat treatment of wheat starch dispersions gives rise to two stages of swelling and solubilization. During the first phase of swelling, solubilized amylose was observed ln the centre of the granules and, to some extent, outside the granules. Further swelling deformed the granules and more amylose was released. When the temperature treatment took place under shear, the outer layer of the swo llen granules fra ctured at 94°C and above, and amylopectin fragments were dispersed into the cont inuous amylose phase. Fragmentation of amylopectin was not observed when samples were heated with a minimum of mechanical action. There were also differences in the final gel structure between samples due to the mechanical treatment during preparation.

Aggregation of amylose took place on cooling and could be observed as irregularities in the gel structure. When the amount of released amylose was limited during the initial phase of swelling and below the critical concentration for gel formation, cooling resulted in deposition of amylose at the surface of the granules. This was expected to have an impact on the behaviour of the granules on further processing.

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